216 PHYSIOLOGY OF MUSCLES AND NERVES. 



aud oblique cross-sections, such as we made in the case 

 of muscle ; nor can phenomena due to the oblique course 

 of the fibres be detected, as in muscle. Where hu-ger 

 masses of nerve-substance occur, as in the dorsal mar- 

 row and brain, the course of the fibres is so complex 

 that nothing can be affirmed except that the cross- 

 sections are always negative in distinction from the 

 natural upper surface or longitudinal section. 



2. If a current is conducted from any two points en 

 the longitudinal section of a nerve, or from one point 

 on the longitudinal section or one on the cross-section, 

 and if the nerve is then irritated, the nerve-current 

 evidently becomes weaker. It does not matter what 

 form of irritation is used, provided that it is sufficiently 

 strong to cause powerful action in the nerve. It thus 

 appears that in the nerve, as in the muscle, a change 

 in the electric condition is connected with its activity, 

 and that this change is a decrease, or negative variation 

 of the nerve-current. We must now go back to the 

 , statement already made (chap. vii. § 2), that the ac- 

 tive condition of the nerve is not shown by any change 

 in the nerve itself. We then found it necessary, in 

 order to observe the actiorf of 'the nerve, to leave it in 

 undisturbed connection with its muscle. The muscle 

 was used as a reagent, as it were, for the nerve, because 

 in the latter neither optical, chemical, nor any other in- 

 dicable changes could be observed. In its electric quali- 

 ties we have, however, now found a means of testing 

 the condition of the nerve itself. Whatever view is 

 taken as to the causes of electric action in nerves, it 

 is at least certain that every change in the electric con- 

 dition must be founded on a change in the nature or 

 arrangement of the nerve substance ; and that there- 



